Functionalization of living rubbery polymers with nitrones

ABSTRACT

This invention relates to a tire which is comprised of a generally toroidal-shaped carcass with an outer circumferential tread, two spaced beads, at least one ply extending from bead to bead and sidewalls extending radially from and connecting said tread to said beads, wherein said tread is adapted to be ground-contacting, and wherein said tread is a cured the rubber formulation which is comprised of (1) hydroxylamine end-group functionalized rubbery polymer of the structural formula:  
                 
 
wherein P represents polymer chains of the rubbery polymer, and wherein (i) R 1  and R 2  are independently selected from the group consisting of substituted or unsubstituted straight, branched, or cyclic alkylgroups, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkaryl groups, alkoxyl groups, halo-alkyl groups, and combinations thereof; or (ii) R 1  and R 2  taken together with the carbon and nitrogen to which they are attached form a 5 to 8 membered ring; and (2) a filler selected from the group consisting of carbon black and silica.

This is a divisional of U.S. patent application Ser. No. 11/169,996,filed on Jun. 28, 2005 (now pending).

BACKGROUND OF THE INVENTION

Metals from Groups I and II of the periodic table are commonly used toinitiate the polymerization of monomers into polymers. For example,lithium, barium, magnesium, sodium, and potassium are metals that arefrequently utilized in such polymerizations. Initiator systems of thistype are of commercial importance because they can be used to producestereo regulated polymers. For instance, lithium initiators can beutilized to initiate the anionic polymerization of isoprene intosynthetic polyisoprene rubber or to initiate the polymerization of1,3-butadiene into polybutadiene rubber having the desiredmicrostructure.

The polymers formed in such polymerizations have the metal used toinitiate the polymerization at the growing end of their polymer chainsand are sometimes referred to as living polymers. They are referred toas living polymers because their polymer chains which contain theterminal metal initiator continue to grow or live until all of theavailable monomer is exhausted. Polymers that are prepared by utilizingsuch metal initiators normally have structures which are essentiallylinear and normally do not contain appreciable amounts of branching.

Rubbery polymers made by living polymerization techniques are typicallycompounded with sulfur, accelerators, antidegradants, a filler, such ascarbon black, silica or starch, and other desired rubber chemicals andare then subsequently vulcanized or cured into the form of a usefularticle, such as a tire or a power transmission belt. It has beenestablished that the physical properties of such cured rubbers dependupon the degree to which the filler is homogeneously dispersedthroughout the rubber. This is in turn related to the level of affinitythat filler has for the particular rubbery polymer. This can be ofpractical importance in improving the physical characteristics of rubberarticles which are made utilizing such rubber compositions. For example,the rolling resistance and traction characteristics of tires can beimproved by improving the affinity of carbon black and/or silica to therubbery polymer utilized therein. Therefore, it would be highlydesirable to improve the affinity of a given rubbery polymer forfillers, such as carbon black and silica.

In tire tread formulations better interaction between the filler and therubbery polymer results in lower hysteresis and consequently tires madewith such rubber formulations have lower rolling resistance. Low tandelta values at 60° C. are indicative of low hysteresis and consequentlytires made utilizing such rubber formulations with low tan delta valuesat 60° C. normally exhibit lower rolling resistance. Better interactionbetween the filler and the rubbery polymer in tire tread formulationsalso typically results higher tan delta values at 0° C. which isindicative of better traction characteristics.

The interaction between rubber and carbon black has been attributed to acombination of physical absorption (van der Waals force) andchemisorption between the oxygen containing functional groups on thecarbon black surface and the rubber (see D. Rivin, J. Aron, and A.Medalia, Rubber Chem. & Technol. 41, 330 (1968) and A. Gessler, W. Hess,and A Medalia, Plast. Rubber Process, 3, 141 (1968)). Various otherchemical modification techniques, especially for styrene-butadienerubber made by solution polymerization (S—-SBR), have also beendescribed for reducing hysteresis loss by improving polymer-fillerinteractions. In one of these techniques, the solution rubber chain endis modified with aminobenzophenone. This greatly improves theinteraction between the polymer and the oxygen-containing groups on thecarbon black surface (see N. Nagata, Nippon Gomu Kyokaishi, 62, 630(1989)). Tin coupling of anionic solution polymers is another commonlyused chain end modification method that aids polymer-filler interactionsupposedly through increased reaction with the quinone groups on thecarbon black surface. The effect of this interaction is to reduce theaggregation between carbon black particles which in turn, improvesdispersion and ultimately reduces hysteresis.

U.S. Pat. No. 4,935,471 (to Adel F. Halasa et al.) discloses a means forcapping living polydiene rubbers in order to improve their affinity forcarbon black. The capped rubbery polymers made by this technique arereported to be useful in manufacturing tire treads which have lowerlevel of rolling resistance and better traction characteristics. Thispatent more specifically discloses polydiene rubber having a high levelof affinity for carbon black which is comprised of polymer chains havingrepeat units which are derived from at least one conjugated diolefinmonomer wherein said polymer chains are terminated with a memberselected from the group consisting of cyanide groups and heterocyclicaromatic nitrogen containing groups. U.S. Pat. No. 4,935,471 alsoreveals a process for preparing a polydiene rubber having a high levelof affinity for carbon black which comprises reacting a metal terminatedpolydiene with a capping agent selected from the group consisting of (a)halogenated nitrites having the structural formula X-A-C≡N wherein Xrepresents a halogen atom and wherein A represents an alkylene groupcontaining from 1 to 20 carbon atoms, (b) heterocyclic aromatic nitrogencontaining compounds, and (c) alkyl benzoates.

Perhaps more interesting from a chemistry perspective are the persistentliterature references to rubber “additives” that improve vulcanizateproperties such as fatigue, dynamic modulus and hysteresis loss bymodifying the polymer-filler interaction (see A Zyusin et al., Intenat.Poly. Sci. & Tech., 11 (2), T/56 (1984); A Payne et al., J. Rubber Res.Inst. Malaya, 22, 275 (1969); H Leeper et.al., Rubber World, 135, 413(1956); A Lykin et.al., Rubber Chem. & Technol., 46, 575 (1973); AKlasek et al., J. Applied Poly. Sci., 61, 1137 (1996); V. Strygin etal., Internat. Poly. Sci. & Tech., 24 (3), T/14 (1997); K Tada et.al.,J. Applied Poly. Sci., 15, 117 (1971); D Graves, Rubber Chem. &Technol., 66, 62 (1993); and L Gonzalez et al., Rubber Chem. & Technol.,69, 266 (1996)).

One of the first additives seen to have such an effect wasp-nitrosodiphenylamine (PNDPA). This material was originally developedby scientists from the Natural Rubber Producers Research Association,(NRPRA), for its antioxidant activity and its ability to chemically bindto the polyisoprene structure through the nitroso group (see A Payne etal., J. Rubber Res. Inst. Malaya, 22, 275 (1969). Subsequent extensivework by Russian scientists, however, discovered that polyisoprenemodified with PNDPA during mixing ultimately decreases hysteresis lossin vulcanizates and improves the green strength of the mixes. While itwas clear from bound rubber measurements and other techniques that therewas a preferential adsorption of the modified macromolecules on thesurface of the carbon black, the nature of the bonding could not beclearly determined with the analytical tools of the time.

Nitrones are useful intermediates in a wide variety of applications. Forexample, nitrones are important as intermediates in organic synthesis,particularly in [3+2] cyclo addition reactions. Nitrones are excellent1,3-dipoles and capable of reacting with double and triple bonds to form5-membered heterocyclic ring structures. For example, isoxazolines andisoxazoles are formed by reacting nitrones with carbon-carbon double andtriple bonds respectively. Accordingly, nitrones have been utilized forsynthesizing various nitrogen containing biologically active compounds,for example, antibiotics, alkyloids, amino sugars, and beta-lactams.

In addition, nitrones are also known for their ability to act asefficient free radical “spin traps”. Nitrones behave as spin trappingagents when a diamagnetic nitrone (the spin trap) reacts with atransient free radical (having a spin) to provide a more stable freeradical (referred to as the spin adduct). More specifically, a veryreactive oxygen-centered or carbon-centered free radical reacts with thenitrone to generate a new and very stable nitroxide radical adduct. Theradical adduct generated may be detectable by electron para-magneticresonance (EPR) spectroscopy if the stabilized free radical has areasonable lifetime. Further, information about a spin of a radical canbe gleaned from a study of the structure and spectroscopiccharacteristics of the new radical adduct due to the increased radicalstability and lifetime. Thus, techniques utilizing nitrone spin trappingagents are an important method for garnering information on freeradicals otherwise difficult or impossible to detect by directspectroscopic observation due to their exceedingly short lifetimes andlow concentrations.

Techniques utilizing nitrone spin trapping agents are also useful forstudying free radical responses in biological systems. For example, thetoxicity of a synthetic beta amyloid peptide preparation towardsglutamine synthesis could be correlated with the characteristics of anEPR signal generated by the spin adduct formed from each batch ofsynthetic beta amyloid peptide and spin trap. U.S. Pat. No. 6,107,315discloses the use of a spin trapping reagent, such asα-phenyl-N-tert-butyl nitrone (PBN), in a suitable pharmaceuticalcarrier for administration to a patient for the treatment of symptomsassociated with aging or other conditions associated with oxidativetissue damage. U.S. Pat. No. 5,723,502 discloses a method forameliorating a cellular dysfunction of a tissue, such as the cosmetictreatment of hair loss and stimulation of hair growth, by administeringa nitrone spin trap, such as PBN, to the affected tissue.

Nitrones have also been found to be useful as agents for controlled freeradical polymerization. More specifically, the presence of a stablenitrone free radical during the polymerization or copolymerization ofmonomers provides for control of polymerization and results in polymershaving a relatively narrow polydispersity, relative to polymers formedin the absence of a stable nitrone free radical. For example, U.S. Pat.No. 6,333,381 discloses the use of PBN to control the polymerizationused in the synthesis of various types of rubbers.

SUMMARY OF THE INVENTION

The subject invention provides a low cost means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. Such functionalizedpolymers can be beneficially used in manufacturing tires and otherrubber products where improved polymer/filler interaction is desirable.In tire tread compounds this can result in lower polymer hysteresiswhich in turn can provide a lower level of tire rolling resistance.

The present invention more specifically discloses a process forpreparing a polydiene rubber having a high level of affinity for fillerswhich comprises reacting a metal terminated polydiene rubber with anitrone. The metal will typically be lithium and the polydiene rubberwill normally be a polybutadiene rubber, a polyisoprene rubber, astyrene-butadiene rubber, a styrene-isoprene-butadiene rubber, anisoprene-butadiene rubber, or a styrene-isoprene rubber.

The subject invention further reveals a hydroxylamine end-groupfunctionalized rubbery polymer which is comprised of polymer chains ofthe structural formula:

wherein P represents polymer chains of the rubbery polymer, and wherein(i) R¹ and R² are independently selected from the group consisting ofsubstituted or unsubstituted straight, branched, or cyclic alkyl groups,alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkarylgroups, alkoxyl groups, halo-alkyl groups, and combinations thereof; or(ii) R¹ and R² taken together with the carbon and nitrogen to which theyare attached form a 5 to 8 membered ring.

The subject invention also discloses a rubber formulation which iscomprised of (1) a hydroxylamine end-group functionalized rubberypolymer which is comprised of polymer chains of the structural formula:

wherein P represents polymer chains of the rubbery polymer, and wherein(i) R¹ and R² are independently selected from the group consisting ofsubstituted or unsubstituted straight, branched, or cyclic alkyl groups,alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkarylgroups, alkoxyl groups, halo-alkyl groups, and combinations thereof, or(ii) R¹ and R² taken together with the carbon and nitrogen to which theyare attached form a 5 to 8 membered ring, and (2) a filler selected fromthe group consisting of carbon black and silica.

The subject invention further discloses a tire which is comprised of agenerally toroidal-shaped carcass with an outer circumferential tread,two spaced beads, at least one ply extending from bead to bead andsidewalls extending radially from and connecting said tread to saidbeads, wherein said tread is adapted to be ground-contacting, andwherein said tread is a cured the rubber formulation which is comprisedof (1) hydroxylamine end-group functionalized rubbery polymer of thestructural formula:

wherein P represents polymer chains of the rubbery polymer, and wherein(i) R¹ and R² are independently selected from the group consisting ofsubstituted or unsubstituted straight, branched, or cyclic alkyl groups,alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkarylgroups, alkoxyl groups, halo-alkyl groups, and combinations thereof; or(ii) R¹ and R² taken together with the carbon and nitrogen to which theyare attached form a 5 to 8 membered ring; and (2) a filler selected fromthe group consisting of carbon black and silica.

DETAILED DESCRIPTION OF THE INVENTION

The subject invention provides a means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. The process of thepresent invention can be used to functionalize any living polymer whichis terminated with a metal of group I or II of the periodic table. Thesepolymers can be produced utilizing techniques that are well known topersons skilled in the art. The metal terminated rubbery polymers thatcan be functionalized with nitrones in accordance with this inventioncan be made utilizing monofunctional initiators having the generalstructural formula P-M, wherein P represents a polymer chain and whereinM represents a metal of group I or II. The metal initiators utilized inthe synthesis of such metal terminated polymers can also bemultifunctional organometallic compounds. For instance, difunctionalorganometallic compounds can be utilized to initiate suchpolymerizations. The utilization of such difunctional organometalliccompounds as initiators generally results in the formation of polymershaving the general structural formula M-P-M, wherein P represents apolymer chain and wherein M represents a metal of group I or II. Suchpolymers which are terminated at both of their chain ends with a metalfrom group I or II also can be reacted with nitrones to functionalizeboth of their chain ends. It is believed that utilizing difunctionalinitiators so that both ends of the polymers chain can be functionalizedwill the nitrone can further improve interaction with fillers, such ascarbon black and silica.

The initiator used to initiate the polymerization employed insynthesizing the living rubbery polymer that is functionalized inaccordance with this invention is typically selected from the groupconsisting of barium, lithium, magnesium, sodium, and potassium. Lithiumand magnesium are the metals that are most commonly utilized in thesynthesis of such metal terminated polymers (living polymers). Normally,lithium initiators are more preferred.

Organolithium compounds are the preferred initiators for utilization insuch polymerizations. The organolithium compounds which are utilized asinitiators are normally organo monolithium compounds. The organolithiumcompounds which are preferred as initiators are monofunctional compoundswhich can be represented by the formula: R—Li, wherein R represents ahydrocarbyl radical containing from 1 to about 20 carbon atoms.Generally, such monofunctional organolithium compounds will contain from1 to about 10 carbon atoms. Some representative examples of preferredbutyllithium, secbutyllithium, n-hexyllithium, n-octyllithium,tertoctyllithium, n-decyllithium, phenyllithium, 1-naphthyllithium,4-butylphenyllithium, p-tolyllithium, 4-phenylbutyllithium,cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium. Secondary-butyllithium is a highly preferredorganolithium initiator. Very finely divided lithium having an averageparticle diameter of less than 2 microns can also be employed as theinitiator for the synthesis of living rubbery polymers that can befunctionalized with nitrones in accordance with this invention. U.S.Pat. No. 4,048,420, which is incorporated herein by reference in itsentirety, describes the synthesis of lithium terminated living polymersutilizing finely divided lithium as the initiator. Lithium amides canalso be used as the initiator in the synthesis of living polydienerubbers (see U.S. Pat. No. 4,935,471 the teaching of which areincorporated herein by reference with respect to lithium amides that canbe used as initiators in the synthesis of living rubbery polymer).

The amount of organolithium initiator utilized will vary depending uponthe molecular weight which is desired for the rubbery polymer beingsynthesized as well as the precise polymerization temperature which willbe employed. The precise amount of organolithium compound required toproduce a polymer of a desired molecular weight can be easilyascertained by persons skilled in the art. However, as a general rulefrom 0.01 to 1 phm (parts per 100 parts by weight of monomer) of anorganolithium initiator will be utilized. In most cases, from 0.01 to0.1 phm of an organolithium initiator will be utilized with it beingpreferred to utilize 0.025 to 0.07 phm of the organolithium initiator.

Many types of unsaturated monomers which contain carbon-carbon doublebonds can be polymerized into polymers using such metal catalysts.Elastomeric or rubbery polymers can be synthesized by polymerizing dienemonomers utilizing this type of metal initiator system. The dienemonomers that can be polymerized into synthetic rubbery polymers can beeither conjugated or nonconjugated diolefins. Conjugated diolefinmonomers containing from 4 to 8 carbon atoms are generally preferred.Vinyl-substituted aromatic monomers can also be copolymerized with oneor more diene monomers into rubbery polymers, for examplestyrene-butadiene rubber (SBR). Some representative examples ofconjugated diene monomers that can be polymerized into rubbery polymersinclude 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethyl-1,3-butadiene, 2-methyll,3-pentadiene,2,3-dimethyl-1,3-pentadiene, 2-phenyl-1,3-butadiene, and4,5-diethyl-1,3-octadiene. Some representative examples ofvinyl-substituted aromatic monomers that can be utilized in thesynthesis of rubbery polymers include styrene, 1-vinylnapthalene,3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene,2,4,6-trimethylstyrene, 4-dodecylstyrene,3-methyl-5-normal-hexylstyrene, 4-phenylstyrene,2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene,3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene, 6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene, α-methylstyrene, and thelike.

The metal terminated rubbery polymers that are functionalized withnitrones in accordance with this invention are generally prepared bysolution polymerizations that utilize inert organic solvents, such assaturated aliphatic hydrocarbons, aromatic hydrocarbons, or ethers. Thesolvents used in such solution polymerizations will normally containfrom about 4 to about 10 carbon atoms per molecule and will be liquidsunder the conditions of the polymerization. Some representative examplesof suitable organic solvents include pentane, isooctane, cyclohexane,normal-hexane, benzene, toluene, xylene, ethylbenzene, tetrahydrofuran,and the like, alone or in admixture. For instance, the solvent can be amixture of different hexane isomers. Such solution polymerizationsresult in the formation of a polymer cement (a highly viscous solutionof the polymer).

The metal terminated living rubbery polymers utilized in the practice ofthis invention can be of virtually any molecular weight. However, thenumber average molecular weight of the living rubbery polymer willtypically be within the range of about 50,000 to about 500,000. It ismore typical for such living rubbery polymers to have number averagemolecular weights within the range of 100,000 to 250,000.

The metal terminated living rubbery polymer can be functionalized bysimply adding a stoichiometric amount of a nitrone to a solution of therubbery polymer (a rubber cement of the living polymer). In other words,approximately one mole of the nitrone is added per mole of terminalmetal groups in the living rubbery polymer. The number of moles of metalend groups in such polymers is assumed to be the number of moles of themetal utilized in the initiator. It is, of course, possible to addgreater than a stoichiometric amount of the nitrone. However, theutilization of greater amounts is not beneficial to final polymerproperties. Nevertheless, in many cases it will be desirable to utilizea slight excess of the nitrone to insure that at least a stoichiometricamount is actually employed or to control the stoichiometry of thefunctionalization reaction. In most cases from about 0.8 to about 1.1moles of the nitrone will be utilized per mole of metal end groups inthe living polymer being treated. In the event that it is not desired tofunctionalize all of the metal terminated chain ends in a rubberypolymer then, of course, lesser amounts of the nitrone can be utilized.

Nitrones will react with the metal terminated living rubbery polymerover a very wide temperature range. For practical reasons thefunctionalization of such living rubbery polymers will normally becarried out at a temperature within the range of 0° C. to 150° C. Inorder to increase reaction rates, in most cases it will be preferred toutilize a temperature within the range of 20° C. to 100° C. withtemperatures within the range of 50° C. to 80° C. being most preferred.The capping reaction is very rapid and only very short reaction timeswithin the range of 0.5 to 4 hours are normally required. However, insome cases reaction times of up to about 24 hours may be employed toinsure maximum conversions.

The nitrones which are used in the practice of this invention are of thegeneral structural formula:

wherein R¹ and R², are independently selected from the group consistingof substituted or unsubstituted straight, branched, or cyclic alkylgroups, alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups,alkaryl groups, alkoxyl groups, halo-alkyl groups, and combinationsthereof. Alternatively, R¹ and R² taken together with the carbon andnitrogen to which they are attached form a 5 to 8 membered ring.

The nitrone used in the practice of this invention will typically be ofthe structural formula:

wherein R⁵, R⁶, R⁷, R₈ and R⁹ are independently selected from the groupconsisting of H, substituted or unsubstituted straight, branched, orcyclic alkyl groups, alkenyl groups, alkynyl groups, aryl groups,heteroaryl groups, alkaryl groups, alkoxyl groups, halogen atoms, cyanogroups, nitro groups, and combinations thereof, alternatively any twoadjacent R⁵, R⁶, R⁷, R⁸ and R⁹ groups taken together with the carbons towhich they are attached can form a 5 to 8 membered ring including 0 to 2heteroatoms selected from the group consisting of oxygen, nitrogen, andsulfur, and wherein R¹⁰ is a substituted or unsubstituted straight,branched, or cyclic alkyl group.

Derivatives of nitrones having the functional core depicted in formula(I) or formula (VII) can also be used in the practice of this invention.The term “derivative”, as used herein, is intended to refer to acompound resulting when one or more desirable substitutions are attachedto the core compound of formula (I) or Formula (VII). To this end, theterm “nitrone derivative”, as used herein, is intended to refer tocompounds having a nitrone functional core, as illustrated in thegeneral formula (I) and general formula (VII). Accordingly, the term“nitrone derivatives” encompass all compounds formed where the R groupsubstitutions of the general formulae (I) and (VII) are independentlyselected from substituted or unsubstituted straight, branched, or cyclicalkyl groups, alkenyl groups, alkynyl groups, aryl groups, heteroarylgroups, alkaryl groups, alkoxyl groups, haloalkyl groups, andcombinations thereof, while the R group substitutions of formulae (VII)above may further include cyano and nitro substitutions. The term“alkyl”, as used herein, is intended to refer to monovalent, saturatedgroups that are straight, branched or cyclic in structure and maycomprise only carbon atoms, such as from 1 to about 10 carbon atoms, ormay also include heteroatoms, such as for example, nitrogen (N), oxygen(O), and sulfur (S). For example, the alkyl substitution ofalpha-phenyl-N-tert-butyl nitrone (PBN) is a tert-butyl group (abranched alkyl) attached to the nitrogen atom of the nitrone functionalcore. Examples of other alkyl groups include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, n-hexyl, n-octyl, tert-octyl and the like.The alkyl substitution may further include generally non-reactivefunctional groups, such as a ketone, an ether, an ester, and an amide.The term “alkenyl”, as used herein, is intended to refer to unsaturatedorganic substitutions having one or more double bonds in the structure.Examples of alkenyl groups include, without limitation, ethenyl(—CH═CH₂), n-propenyl (—CH₂CH═CH₂), and isopropenyl (—C(CH₃)═CH₂). Theterm “alkynyl”, as used herein, is intended to refer to unsaturatedorganic substitution having one or more triple bonds in their structure.Examples of alkynyl groups include, without limitation, ethynyl,propargyl, and the like. The term “aryl”, as used herein, is intended torefer to an unsaturated aromatic carbocyclic group from 6 to 14 carbonatoms having a single ring (e.g. phenyl) or multiple rings (e.g.,naphthyl and anthryl). Unless otherwise constrained by the definitionfor the individual substituent, such aryl groups can be optionally besubstituted with from 1 to 3 substituents selected from the groupconsisting of alkyl, alkoxy, alkaryloxy, alkenyl, alkynyl, amino,aminoacyl, amincarbonyl, alkoxycarbonyl, aryl, carboxyl, cycloalkoxy,cyano, halo, hydroxy, nitro, trihalomethyl, thioalkoxy, and the like.The term “heteroaryl”, as used herein, is intended to refer to an arylgroup containing one or more heteroatoms selected from oxygen, nitrogen,and sulfur. Examples of heteroaryl groups include thiazoles, oxazolesand pyridines. The term “heteroaryl” further includes multiple rings,such as fused ring structures (e.g., quinoline). The term “alkaryl”, asused herein, is intended to refer to -alkylene-aryl groups having 1 to20 carbon atoms in the alkylene moiety and from 6 to 14 carbon atoms inthe aryl moiety. Examples of alkaryl groups include, without limitation,benzyl, phenethyl, and the like. The term “alkoxyl”, as used herein, isintended to refer to the group “alkyl-O—”. An ether group wouldconstitute an alkoxyl substitution. Examples of alkoxy groups include,without limitation, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy,tert-butoxy, sec-butoxy, n-pentyloxy, n-hexyloxy and the like. The term“alkaryloxy” refers to —O-alkylene-aryl groups, such as benzyloxy,phenethyloxy, and the like. The term “cyano”, as used herein, isintended to refer to the group —CN. The term “halo” or “halogen”, asused herein, is intended to refer to fluoro, chloro, bromo and iodogroups. The term “nitro” refers to the group —NO₂. It is alsocontemplated that one or more halogens may be substituents on thealkenyl, aklynyl, aryl and heteroaryl groups as well. Accordingly,examples of nitrone derivatives include linear nitrone compounds such asN-alkyl-a-alkyl nitrones (e.g., N-methyl-α-methyl nitrone orN-methyl-α-ethyl nitrone), N-alkyl-α-aryl nitrones (e.g.,N-methyl-α-phenylnitrone, N-ethyl-α-phenylnitrone,N-isopropyl-α-phenylnitrone, N-isobutyl-α-phenylnitrone,N-s-butyl-α-phenylnitrone, N-t-butyl-α-phenylnitrone (PBN),N-t-pentyl-α-phenylnitrone), N-alkyl-α-cycloalkylnitrones (e.g.,compounds corresponding to the N-alkyl-α-arylnitrone listed above suchas N-isopropyl-α-cyclohexylnitrone, N-t-butyl-α-cyclohexynitrone,N-t-penyl-α-cyclohexylnitrone), and N-aryl-α-arylnitrone (e.g.,N-phenyl-α-phenylnitrone).

Alternatively, R¹ and R² of formula (I) may be joined together to form aring structure containing the nitrone core therein. For example, the R¹and R² substitutions may be joined together to form a 5-memberedpyrroline-nitrone or a 6-membered piperidinyl-nitrone derivative. Thering structure including the carbon and nitrogen atoms to which the R¹and R² are attached, respectively, may be as small as a 5-membered ringor as large as an 8-membered ring. Further, it is contemplated hereinthat where R¹ and R² are joined to form a ring structure, the ring maybe one of aromatic, non-aromatic and condensed rings (e.g., quiniline,isoquinoline, indoline, and naphthyl-type nitrone derivatives) andfurther, the same or different carbon atoms each constituting the ringmay be substituted with one or a plurality of substituents, such as analkyl group(s). Accordingly, examples of cyclic nitrone compoundsinclude pyrroline N-oxides (e.g., 1-pyrroline-N-oxide,5,5-dimethyl-1-pyrroline-N-oxide (DMPO),5,5-diethyl-1-pyrroline-N-oxide, 4,4diethyl-1-pyrroline-N-oxide,3,3-dimethyl-1-pyrroline-N-oxide), pyrrole-N-oxide, andpiperazine-N-oxide.

Alternatively, any two adjacent R⁵, R⁶, R⁷, R⁸ and R⁹ groups of formula(VII) taken together with the carbons to which they are attached may bejoined together form ring including 0 to 2 heteroatoms selected from thegroup consisting of oxygen, nitrogen, and sulfur. The ring structureincluding the carbon atoms to which the two R substitutions are attachedmay be as small as a 5-membered ring or as large as an 8-membered ring,fused to the phenyl. Further, it is contemplated herein that where two Rgroups are joined to form a ring structure, the ring may be one ofaromatic, non-aromatic and condensed rings. For example, adjacent Rsubstitutions may be joined together to form an indole or a quinolineheteroaryl as the “aryl” group of the nitrone. Further examples include,without limitation, isoquinoline, indoline, and naphthyl fused ringsystems. In addition, any of the atoms constituting the ring may besubstituted with one or more substituents, such as an alkyl group(s).

The nitrones of formula (I), formula (VII) and derivatives thereofutilized in the practice of this invention can be efficiently made at arelatively low cost by the procedure described in U.S. Pat. No.6,762,322. The teachings of U.S. Pat. No. 6,762,322 are incorporatedherein by reference in their entirety.

The nitrone will react with the metal terminated polydiene rubber toreplace the metal with a terminal hydroxylamine. The reaction ofN-isopropylphenylnitrone with a living lithium terminated rubberypolymer is depicted as follows:

In this reaction P represents polymer chains of the rubbery polymer. Asis shown, the polymer made having hydroxylamine functional end groupshas good interaction with silica fillers and can easily transform intoother species that have good interaction with carbon black. In any case,the end-group functionalized polymers made by the process of thisinvention are of the general structural formula:

wherein P represents polymer chains of the rubbery polymer, and whereinR¹ and R² are independently selected from the group consisting ofsubstituted or unsubstituted straight, branched, or cyclic alkylgroups,alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkarylgroups, alkoxyl groups, halo-alkyl groups, and combinations thereof.Alternatively, R¹ and R² taken together with the carbon and nitrogen towhich they are attached form a 5 to 8 membered ring.

After the functionalization reaction is completed, it will normally bedesirable to “kill” any living polydiene chains which remain. This canbe accomplished by adding an alcohol, such as methanol or ethanol, tothe polymer cement after the functionalization reaction is completed inorder to eliminate any living polymer that was not consumed by thereaction with the nitrone. The end-group functionalized polydiene rubbercan then be recovered from the solution utilizing standard techniques.

The rubbery compositions of this invention are of particular value inmaking tire tread compounds and in manufacturing tires which arenormally comprised of a generally toroidal-shaped carcass with an outercircumferential tread, two spaced beads, at least one ply extending frombead to bead and sidewalls extending radially from and connecting saidtread to said beads, wherein said tread is adapted to beground-contacting. However, they are also of value for use inmanufacturing other products where good interaction with fillers isdesirable, such as applications where low hysteresis is an advantage.For instance, functionalized rubbers made by utilizing the technique ofthis invention can also be beneficial employed in manufacturing powertransmission belts. In any case, the rubbery composition of thisinvention can be blended with a wide variety of additional ingredientsto attain the desired combination of physical attributes. For instance,it may be desirable to blend one or more resins, such as,coumarone-indene resin into the composition in cases where tire treadsfor high performance tires are being manufactured. The resin willnormally be added in an amount that is within the range of about 5 phrto about 60 phr in race tire applications. In passenger tires that aredesigned for high speed applications, the resin will typically be addedin an amount that is within the range of 2 phr to about 20 phr. Ingeneral purpose passenger tire applications, it is typically preferredfor the tread compound to contain only a small amount (1 phr to 5 phr)of a resin or for the tread formulation to not contain any resin at all.

The functionalized rubbery polymers of this invention can be compoundedutilizing conventional ingredients and standard techniques. Forinstance, the rubber compound will typically also include sulfur,accelerators, waxes, scorch inhibiting agents and processing aids. Inmost cases, the tread rubber formulation will be compounded with sulfurand/or a sulfur containing compound, at least one accelerator, at leastone antidegradant, at least one processing oil, zinc oxide, optionally atackifier resin, optionally a reinforcing resin, optionally one or morefatty acids, optionally a peptizer and optionally one or more scorchinhibiting agents. Such blends will normally contain from about 0.5 to 5phr (parts per hundred parts of rubber by weight) of sulfur and/or asulfur containing compound with 1 phr to 2.5 phr being preferred. It maybe desirable to utilize insoluble sulfur in cases where bloom is aproblem.

The blend will also normally include from 0.1 to 2.5 phr of at least oneaccelerator with 0.2 to 1.5 phr being preferred. Antidegradants, such asantioxidants and antiozonants, will generally be included in the blendin amounts ranging from 0.25 to 10 phr with amounts in the range of 1 to5 phr being preferred. Tire tread rubber formulations made with thefunctionalized rubbers of this invention will also normally contain from0.5 to 10 phr of zinc oxide with 1 to 5 phr being preferred. Theseblends can optionally contain from 0 to 30 phr of tackifier resins, 0 to10 phr of reinforcing resins, 1 to 10 phr of fatty acids, 0 to 2.5 phrof peptizers and 0 to 1 phr of scorch inhibiting agents.

The tire tread rubber formulations of this invention can be used in tiretreads in conjunction with ordinary tire manufacturing techniques. Tiresare built utilizing standard procedures with the tread compound of thisinvention simply being substituted for the rubber compounds typicallyused as the tread rubber. After the tire has been built with the treadformulations of this invention, it can be vulcanized using a normal tirecure cycle. Tires made in accordance with this invention can be curedover a wide temperature range. However, it is generally preferred forthe tires of this invention to be cured at a temperature ranging fromabout 132° C. (270° F.) to about 166° C. (330° F.). It is more typicalfor the tires of this invention to be cured at a temperature rangingfrom about 143° C. (290° F.) to about 154° C. (310° F.). It is generallypreferred for the cure cycle used to vulcanize the tires of thisinvention to have a duration of about 10 to about 14 minutes with a curecycle of about 12 minutes being most preferred.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

EXAMPLE 1

In this experiment N-t-butylphenylnitrone was systhesized utilizing theprocedure described in U.S. Pat. No. 6,762,322. In the procedure used adry 3-liter, 3-necked, round bottom flask equipped with a mechanicalpaddle stirrer, a nitrogen gas flow, and a condenser was charged with 87grams (83.5 ml; 0.82 moles) of benzaldehyde and 63 grams (90.5 ml; 0.86moles) of t-butylamine. The mixture was stirred for about 4 hours atroom temperature to allow complete formation ofN-benzylidene-t-butylamine. After removal of the nitrogen gas flow andthe condenser, the reaction flask was evacuated under an aspirator(about 24″ Hg vacuum) for about 15 minutes. The aspirator was detachedand 288 grams (3.428 moles) of sodium bicarbonate followed by 500 ml ofwater and 500 ml of acetone were added to the 3-liter flask. Thecondenser was reattached to the flask and about 600 gm (0.98 moles) ofOxone® oxidizing agent was carefully added portion-wise through apowder-addition funnel to the stirring reaction over a period of about10 minutes. The reaction began to slowly foam from the evolution ofcarbon dioxide and turn to a bluish tinge as the temperature rose toabout 35° C. The reaction was stirred for one hour after the Oxone®oxidizing agent was added, and GC analysis revealed a trace amount ofstarting imine (3.72 minutes) and a large peak representing2-t-butyl-3-phenyl oxaziridine (4.45 minutes).

The reaction mixture was poured into a beaker containing a 2-phasesolution of 3000 ml water and 300 ml toluene. Insoluble salts werefiltered out and the aqueous layer separated in a separatory funnel. Theupper toluene layer was placed in a 1-liter single-neck, round bottomflask and concentrated over a 30-minute period on a rotary evaporator at50° C. under vacuum (about 24″ Hg) to remove traces of acetone andwater. Several silicon carbide boiling chips were added to theconcentrated oxaziridine and the oxaziridine/toluene solution wasrefluxed at 115° C. to 125° C. for 2-3 hours to form the desiredN-t-butylphenylnitrone product. The excess toluene was removed undervacuum and the resulting clear brown liquid N-t-butylphenylnitrone waspoured into a crystallizing dish and placed in a fume hood.Crystallization was almost immediate, affording 113.1 gm of crudecrystalline N-t-butylphenylnitrone (78% theoretical yield).

EXAMPLES 2-7

In this series of experiments living styrene-butadiene rubbers wereend-group functionalized with various nitrones, compounded in carbonblack and silica filled formulations, and evaluated with respect tophysical properties. The living styrene-butadiene rubbers were made in aone-gallon (3.8 liter) batch reactor which was equipped with anagitator, steam heating, and glycol cooling. The polymerizations wereconducted at 65° C. for two hours. The polymer specification was 75%1,3-butadiene and 25% styrene. The polymerizations were initiated withn-butyl lithium and modified with one mole ratio ofN,N,N′,N′-tetramethylethylenediamine (TMEDA) to lithium. The targetMooney large 1/4 range was 40-45, with an onset glass-transitiontemperature of approximately −35° C. All polymerizations were killedwith a slight excess of the nitrone being used as the terminator(1.1:1.0 mole ratio to lithium), followed after a few minutes by aslight excess of ethanol (1.1:1.0 mole ratio to terminator). BHTantioxidant was added to each cement sample at a level of 1.0 phr. Eachsample was dried using a drum dryer. A control (Example 2) was alsocarried out for comparative purposes and was terminated with ethanolrather than a nitrone. The nitrone used to end-group functionalize therubber in each experiment is identified in Table 3 and Table 4.

Each of the end-group functionalized rubber samples and the controlswere compounded with the compositions of the non-productive (withoutcuratives) and productive (with curatives) formulations being shown inTable 2. The amounts shown are in parts by weight. TABLE 2 Carbon BlackRecipe Silica Filled Recipe parts parts Non-productive Non-ProductivePolymer 100.00 Polymer 100.00 Carbon Black 55.00 Silica 60.00 Oil 10.00Coupling Agent (50/50) 9.60 Stearic Acid 3.00 Wax 1.50 Agerite Resin D1.50 Santoflex 13 2.50 antioxidant Stearic Acid 3.00 ProductiveProductive Santocure CBS* 1.20 Wingstay 100 antioxidant 0.50 Sulfur 1.40Zinc Oxide 2.50 Santocure CBS 2.00 1,3-diphenylguanidine (DPG) 1.60Sulfur 1.70*CBS is cyclohexylbenzothiazole sulfenamide

In the case of the formulation that was filled with carbon black,one-half of the rubber was initially added, followed by the addition ofthe pigments, with the remaining one-half of the rubber being addedsubsequently. The oil was added after two minutes of mixing time withmixing being continued until either 5 minutes or until a temperature of300° F. (149° C.) was reached (whichever came first). In the productivestage the sulfur and Santocure CBTS were added by mill mixing.

In the case of the formulation that was filled with silica, there was aninitial rubber breakdown period of 30 seconds which was followed by theaddition of all pigments. After reaching a temperature of 240° F. (116°C.) the oil was added with the mixing speed being increased (ifnecessary) to reach a temperature of 320° F. (160° C.) at which pointthe mixing speed was adjusted to maintain the temperature at 320° F.(160° C.) for 2 minutes. The productive formulation was made by addingthe productive components of the formulation with mixing being carriedout for either 2 minutes or until a temperature of 230° C. (110° C.) wasreached (whichever came first).

The G′@8.33 Hz and tan δ at 60° C. for each of the rubbers that wasfunctionalized with a nitrone and the controls are reported in Table 3.In Example 2 the styrene-butadiene rubber was not functionalized andserves as a control. Table 3 reports the G′@8.33 Hz and tan δ at 60° C.for the carbon black filled formulations. Table 4 reports the G′@8.33 Hzand tan δ at 60° C. for the silica filled formulations. TABLE 3 CarbonBlack Filled Styrene-Butadiene Rubber Formulations Example NitroneG′@8.33 Hz Tan δ at 60° C. 2 none 511.43 0.204 3 N-t-butylphenylnitrone529.14 0.187 4 N-isopropylphenylnitrone 570.2 0.178 5 N-isopropyl-4-544.49 0.192 dimethylaminophenylnitrone 6 diphenylnitrone 519.34 0.193 7N-isopropyl-4- 615.95 0.161 pyrrolidinophenylnitrone

TABLE 4 Silica Filled Styrene-Butadiene Rubber Formulations ExampleNitrone G′@8.33 Hz Tan δ at 60° C. 2 none 497.53 0.124 3N-t-butylphenylnitrone 487.02 0.121 4 N-isopropylphenylnitrone 502.140.109 5 N-isopropyl-4- 480.82 0.119 dimethylaminophenylnitrone 6diphenylnitrone 427.8 0.110 7 N-isopropyl-4- 524.47 0.107pyrrolidinophenylnitrone

A low tan δ value at 60° C. is indicative of low rolling resistance andgood tire tread wear characteristics. As can be seen by reviewing Table3 and Table 4 all of the rubber samples that were filled with bothcarbon black and silica exhibited lower tan δ values at 60° C. than didthe controls. This shows that nitrones can be used to functionalizerubbery polymers used in tire tread formulations to improve rollingresistance and tire tread wear characteristics.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

1. A hydroxylamine end-group functionalized rubbery polymer which iscomprised of polymer chains of the structural formula:

wherein P represents polymer chains of the rubbery polymer, and wherein(i) R¹ and R² are independently selected from the group consisting ofsubstituted or unsubstituted straight, branched, or cyclic alkylgroups,alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkarylgroups, alkoxyl groups, halo-alkyl groups, and combinations thereof, or(ii) R¹ and R² taken together with the carbon and nitrogen to which theyare attached form a 5 to 8 membered ring.
 2. A hydroxylamine end-groupfunctionalized rubbery polymer as specified in claim 1 wherein thepolymer chains of the rubbery polymer are comprised of repeat units thatare derived from a conjugated diolefin monomer containing from 4 to 8carbon atoms.
 3. A hydroxylamine end-group functionalized rubberypolymer as specified in claim 1 wherein the polymer chains of therubbery polymer are comprised of repeat units that are derived from1,3-butadiene.
 4. A hydroxylamine end-group functionalized rubberypolymer as specified in claim 3 wherein the polymer chains of therubbery polymer are further comprised of repeat units that are derivedfrom styrene.
 5. A hydroxylamine end-group functionalized rubberypolymer as specified in claim 1 wherein R¹ represents a phenyl group. 6.A hydroxylamine end-group functionalized rubbery polymer as specified inclaim 5 wherein R² represents an isopropyl group.
 7. A rubberformulation which is comprised of (1) the hydroxylamine end-groupfunctionalized rubbery polymer specified in claim 1, and (2) a fillerselected from the group consisting of carbon black and silica.
 8. Ahydroxylamine end-group functionalized rubbery polymer as specified inclaim 1 wherein the polymer chains of the rubbery polymer are comprisedof repeat units that are derived from isoprene.
 9. A hydroxylamineend-group functionalized rubbery polymer as specified in claim 3 whereinthe polymer chains of the rubbery polymer are further comprised ofrepeat units that are derived from a vinyl aromatic monomer selectedfrom the group consisting of styrene, 1-vinylnapthalene,3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene,2,4,6-trimethylstyrene, 4-dodecylstyrene,3-methyl-5-normal-hexylstyrene, 4-phenylstyrene,2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene,3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene,6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene, andα-methylstyrene.
 10. A hydroxylamine end-group functionalized rubberypolymer as specified in claim 1 wherein the hydroxylamine end-groupfunctionalized rubbery polymer has a number average molecular weightwhich is within the range of 50,000 to 500,000.
 11. A hydroxylamineend-group functionalized rubbery polymer as specified in claim 1 whereinthe hydroxylamine end-group functionalized rubbery polymer has a numberaverage molecular weight which is within the range of 100,000 to250,000.
 12. A tire which is comprised of a generally toroidal-shapedcarcass with an outer circumferential tread, two spaced beads, at leastone ply extending from bead to bead and sidewalls extending radiallyfrom and connecting said tread to said beads, wherein said tread isadapted to be ground-contacting, and wherein said tread is a cured therubber formulation which is comprised of (1) hydroxylamine end-groupfunctionalized rubbery polymer of the structural formula:

wherein P represents polymer chains of the rubbery polymer, and wherein(i) R¹ and R² are independently selected from the group consisting ofsubstituted or unsubstituted straight, branched, or cyclic alkylgroups,alkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, alkarylgroups, alkoxyl groups, halo-alkyl groups, and combinations thereof; or(ii) R¹ and R² taken together with the carbon and nitrogen to which theyare attached form a 5 to 8 membered ring; and (2) a filler selected fromthe group consisting of carbon black and silica.
 13. A tire as specifiedin claim 12 wherein the polydiene rubber is selected from the groupconsisting of polybutadiene rubber, polyisoprene rubber,styrene-butadiene rubber, styrene-isoprene-butadiene rubber,isoprene-butadiene rubber, and styrene-isoprene rubber.
 14. A tire asspecified in claim 12 wherein the tread is further comprised of acoumarone-indene resin.
 15. A tire as specified in claim 14 wherein thecoumarone-indene resin is present in the tread at a level which iswithin the range of 5 phr to 60 phr.
 16. A tire as specified in claim 12wherein R¹ represents a phenyl group.
 17. A tire as specified in claim16 wherein R² represents an isopropyl group.
 18. A tire as specified inclaim 12 wherein the polymer chains of hydroxylamine end-groupfunctionalized rubbery polymer are comprised of repeat units that arederived from 1,3-butadiene.
 19. A tire as specified in claim 18 whereinthe polymer chains of the hydroxylamine end-group functionalized rubberypolymer are further comprised of repeat units that are derived fromstyrene.
 20. A tire as specified in claim 19 wherein the hydroxylamineend-group functionalized rubbery polymer has a number average molecularweight which is within the range of 50,000 to 500,000.